Apparatus for testing auto electronics systems

ABSTRACT

An interactive system and method for testing vehicle electronics systems is disclosed in which various vehicle subsystems are exercised under the control of the tester unit while the performance of associated subsystems are monitored to detect and isolate malfunctions. The tester includes interchangeable program cartridges that can be easily inserted to adapt the unit for a variety of different vehicles and test procedures, and also optional interchangeable input/output cartridges for test procedures in which additional access to or from the tester or peripheral devices is necessary. The test unit accesses the vehicle&#39;s electronics data bus by means of an assembly line diagnostic link, the access being accomplished via a multiplexer that makes it possible to locate faults on the data bus itself. The tester greatly reduces the time and effort necessary to analyze malfunctions in the field, and is considerably more comprehensive than prior test equipment.

BACKGROUND OF THE INVENTON

1. Field of the Invention

This invention relates to automobile testing equipment and methods, andmore particularly to the diagnostic testing of automobile electronicssystems.

2. Description of the Prior Art

As the use of electronics to control and perform various automotivefunctions becomes more prevalent, the quick, accurate and comprehensivetesting of automotive electronics systems has grown to be more of aproblem. (The term "automobile" as used herein includes trucks and othervehicles having electronics systems analogous to those found inautomobiles.) Currently available field test equipment is generallypassive in nature. The testers monitor the outputs of variouselectronics systems in the automobile for a given operating condition,such as the motor idling, in an attempt to determine the cause of amalfunction. However, it may not be possible to determine the cause ofmany malfunctions without taking the automobile through a sequence ofoperating conditions, such as starting the engine and accelerating to ahigh speed, and simultaneously observing the condition of theelectronics systems during the testing sequence. Available testers donot have any convenient mechanism for sequencing an automobile through avariety of operating conditions, and are generally limited in the numberof different responses they can observe.

The inability to perform comprehensive diagnostic testing of electronicssystems at the local site level can result in great inefficiencies. Forexample, it is often difficult to determine whether a particular problemresides in the engine or the transmission. Of transmissions which areshipped back to the factory for correction, the majority are returnedwith no problem having been located, while in most of the remainder theproblem is corrected by a minor adjustment at the factory that couldhave been made in the field had the proper diagnostic equipment beenavailable.

Another complicating factor in electronics testing is the proliferationof many different electronics systems for different makes of cars, amongdifferent models from the same automotive manufacturer, and even annualchanges within the same model line. The different electronics systemsare generally accompanied by different data formats that limit anyparticular testing unit to only a relatively small number of vehicles.Stocking a large number of different monitors to accommodate the variousmakes and models is expensive, inefficient and wasteful. However, due tothe complexity of current electronics systems, it is difficult andsometimes impossible to perform adequate field service without the useof proper electronic testers.

The proliferation of different electronics systems is not limited todifferent makes and models; often the same model car will employsignificantly different data formats with each successive model year.This rapidly obsoletes testers which are dedicated to any particularmake or model.

Another problem is the difficulty in simulating normal drivingconditions within the confines of an automotive repair shop, while atthe same time monitoring the various electronics systems to determinethe location and nature of any malfunctions. Also, some automotiveproblems are intermittent and do not show up in a single test run.Current testers do not have the capability of monitoring a vehicle'sperformance over a long period of time and capturing the status of thevarious electronics systems when an intermittent malfunction occurs soas to enable effective diagnostic analysis.

SUMMARY OF THE INVENTION

In view of the above problems associated with the prior art, it is anobject of the present invention to provide a novel and improved testingunit and method for automotive electronics systems which provides forboth passive monitoring of the various systems, and for the activeexercising and control of a particular system and the simultaneousmonitoring of associated electronics systems to identify anymalfunctions related to the system being tested.

Another object is the provision of such a testing unit in a compact,portable package that can be hand held and either kept at a localtesting site or allowed to travel with the vehicle.

Still another object is the provision of a novel and improved automotiveelectronics tester which can be easily and inexpensively adapted for usewith many different kinds of automobiles having a wide variety ofelectronic data formats.

A further object is the provision of such a testing unit and associatedmethod for continuously monitoring an automobile during normal use andfor activating the unit upon the occurrence of an intermittentmalfunction to locate and diagnose the problem.

These and other objects are accomplished in the present invention bymeans of a diagnostic test unit which includes a microprocessor thatboth controls an active test sequence applied to specified electronicssystems in the automobile and monitors the responses of associatedsystems; a means such as a keyboard for providing operational controlsto the microprocessor; a display for operator real time readout of testresults; a program means for providing diagnostic test sequences to themicroprocessor; a transceiver which provides a two-way interface betweenthe microprocessor and the automobile electronics systems to transmittest signals from the microprocessor for exercising particular systemsin the automobile, and to enable the microprocessor to monitor thecondition of associated systems while the first system is beingexercised; and a power supply for the unit. The tester is adapted toreceive a number of interchangeable program cartridges, each cartridgeproviding desired test sequences for particular makes, models and years.In this way the field test site need only inventory a collection ofsmall and relatively inexpensive cartridges, each of which can beinserted into a single testing unit as needed.

The automobile's internal electronics data bus to which many of itselectronics systems are connected is accessed by connecting the testerto an associated assembly line diagnostic link (ALDL). For automobilesin which the electronics data bus is provided as a ring bus with a pairof output terminals, the tester is connected to both terminals andprovided with a multiplexer which multiplexes test patterns onto bothterminals. Each of the automobile systems on the data bus can thuscontinue to be accessed despite the presence of a fault on the bus, andthe location of the fault can be found by determining the penetration ofeach multiplexed connection.

In a manner similar to the interchangeable memory cartridges, the testeris also adapted to receive a number of different input/outputcartridges. These latter cartridges are used for tests which requireaccessing the automotive electronics both through the assembly linediagnostic link and also at various special test points not on theassembly line data link, or for interfacing with peripheral equipment.An input/output cartridge can also be provided for communicating thetest results to a remote location, such as a central diagnostic center.

In addition, the tester can be used as a portable vehicle data monitorto detect intermittent malfunctions during normal driving. Connected tothe data bus in a low power standby mode, the tester "wakes" itself upwhen it senses data bus activity, and then monitors the activity on thedata bus to capture the status of the various electronics systems inmemory at the moment a malfunction occurs.

These and other features and advantages of the invention will beapparent to those skilled in the art from the following detaileddescription of preferred embodiments, taken together with theaccompanying drawings, in which:

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a portable automobile electronicstesting unit constructed in accordance with the invention;

FIG. 2 is a sectional view taken along the lines 2--2 of FIG. 1;

FIG. 3 is a plan sectional view of a program cartridge used inconnection with the tester;

FIG. 4 is a sectional view taken along the line 4--4 of FIG. 3;

FIGS. 5, 6 and 7 are respectively plan, frontal elevational and sideelevational views of an input/output cartridge used in connection withthe tester;

FIGS. 8 and 9 are respectively plan and side elevational views ofanother input/output cartridge used as a communications interface forthe tester;

FIG. 10 is a block diagram showing the connection of the tester to anautomobile electronics data bus;

FIGS. 11a, 11b and 11c are collectively a flow diagram of the programapplied to the automobile's body computer module to emulate theoperation of various automotive systems and thereby effectively decouplethe master controller from the electronic data bus during testing;

FIG. 12 is a block diagram of the electronic components employed in thetester;

FIG. 13 is a schematic diagram of the circuitry used in the transceiverand multiplexer portions of the tester; and

FIG. 14 is a block diagram of an input/output cartridge used to monitorthe automobile electronics for intermittent malfunctions.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A perspective view of the hand held automotive electronics testerprovided by the present invention is given in FIG. 1. The tester iscontained in a housing 2 that is very convenient to handle, weighingless than 3 pounds and approximately 8 inches long, 3.7 inches wide and1.875 inches deep. A 16 key, multi-function keyboard 4 with tactile feelprovides program instructions to the internal tester electronics. Thefunctions of the various keys depends upon the particular tests beingconducted, but in general the keys can be used to vary the automotivecondition so that the operation of the car's electronics systems can bemonitored under different conditions. For example, for testing with themotor running, the "accelerate" button 6 can be depressed to speed upthe engine, while the "decelerate" button 8 can be depressed to slow theengine down. In general, testing is performed in a pre-programmedsequence, as explained further below, but manual overrides andoperational controls can be input through the keyboard. An alphanumericliquid crystal display 10 provides information on the testing results;the particular information to be displayed can also be controlledthrough the keyboard 4.

The tester includes built-in software routines that are independent ofany particular testing application, and are useful in a variety ofdifferent applications. The built-in routines fall into four categories:executive routines; serial data handling routines; self-test routines;and general utility routines.

In addition to the built-in software, the tester housing includes areceptacle for interchangeable plug-in program cartridges 12. Eachcartridge is programmed to run one or more particular test sequences fora particular automotive model or series of models. After a test sequencehas been completed, the cartridge may simply be removed and replacedwith a different cartridge, thereby making it possible to performdifferent tests on different types of cars having very differentelectronics systems with a single tester and an inventory of inexpensiveprogram cartridges. Some examples of the different types of cartridgesthat can be provided are:

Engine Control Module Testing Cartridge

This test program is similar to conventional passive testing, in whichdata is obtained from the vehicle's engine control module (ECM),including ECM malfunction codes as well as diagnostic data. The datastreams are captured on a scheduled or event-triggered basis, scaled,and displayed in pre-selected or operator selected pairs. Variousreadout modes can be selected by the operator.

System Diagnostic Testing Cartridge

The diagnostic test cartridge has three capabilities: subsystem testing,vehicle service diagnostics, and intermittent or "snapshot" testing. Thesubsystem testing provides the ability to monitor and control all serialdata coming from or going to any specified automotive electronicssubsystem. This allows the technician to decouple the subsystem from thenormal master-directed operation and exercise it independently of allother subsystems. The subsystem tests include:

(1) BCM. A passive monitoring of all normal communications transmittedfrom or received by the master controller, or body computer module(BCM), including data to and from the engine control module (ECM),instrument panel cluster (IPC), heating, ventilation and airconditioning unit (HVAC) and secondary displays.

(2) ECM. In the ECM tests the technician can either monitor ECM serialdata, or control certain ECM discrete outputs. The output controlfunction allows the technician to control such outputs as the torqueconverter clutch, the canister purge solenoid or the idle air controlmotor.

(3) IPC. Such IPC operational data as the fuel gauge or IPC switchclosures can be monitored. The tester can also assume control of theserial data bus and emulate the BCM relative to its control of the IPCto determine whether or not a problem is in the IPC. For example, IPCdisplays can be controlled, display segments tested, and telltailsturned on and off.

(4) HVAC. As with the previous tests, the HVAC test provides thetechnician with the capability of monitoring normal communications withthe HVAC. In the control tests, all of the discrete output commands ofthe HVAC can be controlled such as positioning the air flow doors,engaging/disengaging A/C clutch, and controlling the blower motor speed.

(5) Secondary Display. With this cartridge the tester can monitor datatransmitted to or from each of the displays, as well as control aportion of the function which the devices can display, such as drivingindividual displays or performing display segment tests.

With the vehicle service diagnostic test, the tester is capable ofperforming almost all of the functions performed by the vehicles'on-board service diagnostics, including displaying ECM and BCMmalfunction codes, monitoring assembly line diagnostic link (ALDL)discrete and analog parameters, and controlling ECM and BCM outputs.This cartridge also provides a number of enhancements over the on-boardservice diagnostics.

For intermittent testing, the cartridge enables the tester to monitorvarious subsytems and capture a "snapshot" of the serial data undercertain conditions. These conditions can include the occurrence of aspecified ECM or BCM malfunction code, the occurrence of any ECM or BCMmalfunction code, the occurrence of any malfunction code, or a manualtrigger via the tester keyboard 4. Once the intermittent test triggerhas occurred, the program cartridge enables the technician to selectbetween displaying up to 64 samples of ALDL data before and after thetrigger, including malfunction codes, or displaying the normalcommunication data. The tester can be left in place on the vehicleduring normal operation away from the field service center, with theintermittent test mode used to capture the subsystem conditions upon theoccurrence of a particular intermittent malfunction and thus diagnosethe malfunction.

Functional Test Director Cartridge

This program cartridge contains a functional test director thatautomatically executes a series of engine control tests interactivelywith the service technician. The functional test director provides theservice technician with subsystem-level fault isolation, such as the O₂sensor circuit, fan circuit, etc., by exercising particular subsystemsin turn and concurrently monitoring the condition of associatedsubsystems. When a particular fault has been isolated, the functionaltest director stops executing and notifies the technician of the problemarea, as well as a key into the vehicle's service manual to be used tosolve the problem. Various subsystems or engine problems which may beincluded as part of the fault isolation are: throttle position sensor;reference pulse sensor circuit; park/neutral switch circuit; manifoldair pressure (MAP) sensor; idle arm control (IAC) motor; oxygen sensor;system rich/lean; fan circuit; thermostat.

This program cartridge also allows a subset of the engine control testsexecuted by the functional test director to be executed on an individualbasis by the technician. The individual tests provide the technicianwith the same type of information as the functional test director forthe selected subsytem.

The functional test director is an example of one application of thebasic tester.

Communications Interface Cartridge

This program cartridge provides a standard RS232C interface for thetester which allows the tester to be interfaced with printers, modems,full function keyboards or remote host computers. The cartridge includesa 16 K byte EPROM which controls software that allows for a remotekeyboard operation bypassing the tester keyboard 4 for user-defined keycommands; remote display of the tester display parameters; transmissionof remote host-selected parameters; and transmission of raw, unprocessedvehicle data. With this cartridge an auto can be tested from a remotelocation where better facilities or more trained personnel may belocated.

The cartridge can also be used to debug tester software duringdevelopment via a CRT/keyboard or personal computer by the use ofroutines such as the Motorola "LILbug" debug routine.

Additional Program Cartridges

Further program cartridges which may be inserted into the tester includeones for transmission diagnostics, remote radio/control headdiagnostics, digital volt-ohmmeter, vibration analyzer, multiplex systemexerciser and others. Also, different cartridges may have to be providedto perform the same types of tests on different models or even fordifferent annual versions of the same model.

Continuing with the description of the basic tester shown in FIG. 1, aplug-in connector 14 is inserted into a multiprong input/output socketon the tester and held in place by means of screws on either side of theconnector. A cable 16 extends from the connector and is provided at itsopposite end with another connector (not shown) that connects to thevehicle's electronic data bus via the ALDL. This is the basiccommunications link by which the condition of the various automobilesystems are monitored by the tester, and active signals applied from thetester to exercise selected vehicle systems. Power is also supplied fromthe vehicle cigarette lighter socket via cable 16 to the tester.

In addition to the basic connection between the tester and vehicle viaconnector 14 and cable 16, certain additional tests may be accomplishedby connecting the tester to both the ALDL and a second location on thevehicle, or it may be desired to connect the tester to peripheralinput/output devices such as a modem or printer. For this purpose, asecond receptacle is provided in the tester for a removeableinput/output cartridge 18 that provides the second connection to thevehicle or peripheral device. Examples of test functions that wouldrequire both the ALDL connector and a separate input/output cartridgeinclude hydramatic power train and air conditioner diagnostic testing.

The internal mechanical structure of the tester is shown in FIG. 2. Theinternal electronics are mounted on a main circuit board 20, including atransformer 22 used to supply the tester with power from the vehicle. Aprogram cartridge 12 is shown in place, with its electronics mounted ona circuit board 24 and connected to the tester electronics via an edgeboard connector 26. An input/output cartridge 18 with its electronicsacquires data from its associated cable 28 and provides it to the testerelectronics via an edge board connector 30. A flat cable 31 connects theprogram cartridge 12 and input/output cartridge 18 to the microprocessorbus on the main circuit card 20 via connector 32. Cable 16 is a 12 leadcable which extends from the tester to an ALDL connector 33. In additionto providing a connection to the vehicle ALDL, connector 33 ties two ofthe cable 16 leads to a two-wire coiled cable 34 that connects to acigarette lighter adapter 35. Adaptor 35 plugs into the vehicle'scigarette lighter to provide power to the tester via cable 35, ALDLconnector 32 and cable 16.

Referring now to FIGS. 3 and 4, the principal mechanical features of theprogram cartridges are shown. Each cartridge is provided withspring-biased squeezable latches 36 on each side that can be squeezedinwardly by means of finger pads 38 acting against coil springs 40,permitting the cartridge to be inserted into the receptacle in thetester body 2. The spring-biased latches are then released, latching thecartridge into place in the receptacle. The cartridge is easily removedwhen desired by simply pressing in on finger pads 38 to release thelatch and pulling the cartridge out. To ensure proper placement in thetester, the top of the cartridge is provided with a bracket 42 thatincludes a slot 44 which receives a corresponding locator tab extendingin from the tester.

A special input/output cartridge which provides for a connection withboth the tester ALDL ports and the input/output receptacle is shown inFIGS. 5, 6 and 7. This auxiliary cartridge 45 provides the low powerstandby vehicle data monitor "snapshot" capability referred topreviously. Its forward end includes a pair of latches 46 and fingerpads 47 on either side which releasably connect the cartridge to thetester input/output receptacle. An edge board connector 48 makeselectrical contact with the tester within the receptacle. The upperportion of this specialty input/output cartridge 45 includes a femalesocket 49 which plugs into the corresponding pin socket on the tester inplace of ALDL connector 14, with the ALDL connector reconnected to acorresponding female connector 50 on the rear of cartridge 45. Thisinterception of the ALDL cable is used to provide serial link activitymonitoring and power moding control. In addition, a separate cable isattached to the cartridge at connector 51 to provide the operatortrigger control/indicator operations.

Another input/output cartridge which houses standard RS232communications interface electronics appears in FIGS. 8 and 9. Thiscartridge 18 is similar in outward construction to the program cartridge12, and includes a pair of spring-biased squeezable latches 52 on eachside that can be squeezed inwardly by finger pads 53, permitting thecartridge to be inserted and releasably latched in the tester'sinput/output receptacle. The bottom of the cartridge is provided with abracket 54 that includes a slot 55 which receives a correspondinglocator tab extending in from the tester to ensure proper placement. Anedge board connector 56 at one end of the cartridge makes electricalcontact with the tester within the input/output receptacle, while amultipin socket 57 at its other end receives a communications cable. Aswitch 58 is provided to switch the cartridge between an M mode in whichdata is sent to a peripheral device such as a modem, printer, etc., andat test mode in which the RS232 cartridge is connected to an externalcomputer for developing and debugging test software. An eight positionswitch 59 allows the RS232 data rate to be varied from 160 up to 19,200BAUD.

For other applications requiring a separate input/output cartridge, suchas hydramatic power train, digital volt meter and air conditionerdiagnostics, an input/output cartridge similar in physical constructionto the program cartridge shown in FIGS. 3 and 4 is inserted into thetester's input/output receptacle, with the ALDL connector 14 left inplace.

The manner in which the tester is connected via the ALDL connector to avehicle's electronics data bus is illustrated in FIG. 10. Theelectronics data bus 58 interconnects various vehicle electronicssubsystems, such as BCM 60; ECM 62; HVAC 64; IPC instrument panel 66; asecondary display subsystem 68 consisting of a CRT controller (CRTC), anelectronic climate control panel (ECCP) or a climate control anddiagnostic information center (CCDIC); and a voice module 70.

The vehicle's ALDL 72 is connected onto the electronics data bus 58 forfinal assembly line testing at the factory. It connects to two terminals74, 76 on the data bus. This type of bus, in which the two terminalsform a loop with the various subsystems, is referred to as a "ring" bus.

Prior field electronics testing was generally limited to a passivereadout of the ECM by means of a diagnostic uni-directional serial dataline sourced by the ECM and brought out to the ALDL connector. In thepresent invention, by contrast, the tester 2 is connected to theelectronics bi-directional operational data bus 58 by means of the ALDL72. This is believed to be a unique use of the data bus, which was notdesigned primarily for diagnostics as was the ECM diagnostic serial dataline. The present tester in essence becomes an integral part of theelectronics operational system by connecting onto the data bus. Thisnovel use of the data bus opens up many possibilities for diagnostictesting that could not be performed previously. The tester can be usedto emulate or exercise any of the vehicle's subsystems which areconnected to the data bus, while monitoring the other sub-systems todetect and identify any malfunctions. The ALDL is not believed to havebeen previously used for this type of field testing, and in factorytesting it is believed to have been used only as a one-waycommunications link to read out data from the BCM; the ECM is generallyaccessed in the factory either through the ALDL or directly through theECM.

Applicant's novel approach provides a substantial advantage in thetesting of modern electronics systems, in that many vehicle functionsutilize a number of different electronic subsystems. For example,operating the air conditioning involves five subsystems: ECM 62, HVAC64, IPC 66, ECCP 68 and BCM 60. The identification of the particularsubsystem responsible for an air conditioner malfunction can be verydifficult with conventional testing methods. The present inventionenables each of the subsystems in turn to be exercised while the databus 58 is monitored to quickly and easily determine the location andnature of the problem.

For the tester to gain full control of the electronics data bus 58, theBCM 60 must be effectively decoupled from the bus. However, simplydisconnecting the BCM from the data bus will result in the shutdown ofthe total system operation. Applicant has arrived at the novel solutionof using his program cartridges to load a special program into the BCMwhich keeps it functioning in a slave state but allows the tester totake over control and emulate the other subsystems on the data bus. Thistechnique is employed for the various testing applications which use theBCM. Operating as the master, the tester can emulate any subsystem bysourcing subsystem messages and transmitting them to the othersubsystems. The tester can also read data from any subsystem or controlthe subsystem by sending control data to it.

A flow diagram of the program which is loaded into the BCM is providedin FIGS. 11a-11c. Referring first to FIG. 11a, the BCM emulation startswith the tester executing an External Load (EXTLD) routine which firstdownloads a BOOTLOAD routine from the tester to the BCM RAM memory;loads a second routine, Outcontrol (OUTCNTRL), into the BCM; and thenjumps to execute the desired subsystem control or emulation routine. Thetester waits for an ALDL interrogation message 201 from the BCM. Itissues a "Download Request" message 202 to the BCM and waits for aresponse 203 from the BCM indicating that it is ready for the downloadroutine. The tester then downloads the BOOTLOAD routine 204 into the BCMRAM over the system bus and waits for an ALDL interrogation message 205from the BCM. The tester then issues an "Execute Download" message 206to the BCM over the system bus, delays 100 msec 207, switches the testerfrom the slave mode to the master mode 208, and downloads an OUTCNTRLroutine 209 into the BCM scratchpad RAM via the system bus. When asuccessful download message 210 is received from the BCM, the testerinitiates periodic communication to the OUTCNTRL routine 211 executingin the BCM and then jumps to the desired subsystem emulation or controlroutine 212.

The BOOTLOAD routine which is loaded into the BCM from the tester putsthe BCM into the slave mode waiting for messages from the tester. If amessage is not received within a pre-specified time, the BCM revertsback to the master mode. The function of this routine is to accept datamessages from the tester and store them in scratchpad RAM. The sum ofthese messages constitute an executable routine called OUTCNTRL to whichthe BCM jumps and executes upon successful completion of storing all ofthe routine in RAM.

The execution of BOOTLOAD is shown in FIG. 11b in which first outputcompare timers, time-out timers 213, and serial communicationport/variables 214 are initialized. The BCM monitors the system bus fordata 215 and, if no data is received, it checks to see if it is time totoggle a Computer Operate (COP) timer 219. If the toggle time has notarrived, the BCM returns to monitor for serial data received 215. If itis time to toggle the COP, the COP is toggled 220 to prevent the BCMfrom automatically resetting. The time-out timer is decremented 221 andthen checked to see if the time since the last received valid messagehas exceeded the time limit 222 and, if it has, the BCM jumps to thereset vector 223 where the BCM is reset and assumes normal operation,including control of the system bus. If serial data has been received215 it is checked for validity 216 and, if it is not valid, it isignored and the serial data ports and variables are reinitialized 214.If the data is valid it is saved, and a message sumcheck and bytecounter are updated 217. The message is then checked for completion 218and, if it is complete, the BCM jumps to the loaded OUTCNTRL routine andstarts executing 224.

The OUTCNTRL routine causes the BCM to act as a slave subsystem whichreceives and processes messages from the tester, which operates as themaster. The tester can command the BCM to set its output discretes highor low, to slew its analog outputs, or to read its analog inputs. It canalso command the BCM to go idle, or tell it to quit operating as a slaveand return to its normal operating mode. When executing this routine,the BCM also checks for valid bus activity and will revert back to thenormal operating mode if it does not detect proper activity. Theoperation of OUTCNTROL is shown in FIG. 11c in which it firstinitializes Output compare timer and loss of communication timers 225and then transmits a "Download Acknowledge" message 226 to the tester.It continually checks the timers and periodically toggles the COP 227,and checks to see if communication has been lost at any time 228. Ifcommunication has been lost, the routine jumps to a reset condition 229and starts operating as a normal BCM. If communication is normal, itchecks 230 and processes 231 received data, and checks messages forvalidity 232 in a manner similar to the BOOTLOAD routine. When a validmessage is received the routine processes the message and responds toits command 233, clears the communication loss timer 234, and transmitsa "Command Acknowledge" message 235 to the tester. This sequencecontinues until the tester sends a "Quit" command, at which time the BCMreverts back to its normal operation as system bus master.

Returning to FIG. 10, the tester makes a pair of separate connections tothe ALDL through leads ALDL M and ALDL L. The test signals which areapplied from the tester to the data bus are multiplexed onto these twoleads such that they alternate between the two leads or are delivered toboth simultaneously. This technique is very useful in determining thepresence and location of any faults which may develop on the data bus.For example, assume that a fault appears on the data bus at location 78between the HVAC 64 and IPC 66. The tester can be programmed todetermine that signals on ALDL L penetrate only to HVAC 64, whilesignals on ALDL M penetrate only to IPC 66, or conversely that onlysignals from ECM 62 and HVAC 64 are delivered to ALDL L and only signalsfrom the remaining subsystems are delivered to ALDL M. The location ofthe data bus fault can thus be readily determined. In addition,connection through the ALDL makes it possible to access all of theconnected systems and continue normal testing despite the presence of afault on the data bus.

A block diagram of the tester is provided in FIG. 12. The main circuitcard assembly includes the microprocessor 80, which in the preferredembodiment is based on the Motorola CMOS 6303. The main circuit boardassembly 82 is a two-layer printed wiring board with dual-in-linepackage ICs, chip capacitors and resistors. In addition to themicroprocessor, the main circuit board contains a 4 MHz clock oscillator84, a 64 K on-board ultraviolet EPROM 86, a 64 K scratch pad CMOS RAM88, the keyboard 4 and keyboard encoder 89, an ECM interface 90, an 8192BAUD (bits per second) serial data link transceiver 92 whose impedanceis substantially matched with that of the vehicle electronics data bus,a multiplexer circuit 94 connected to the transceiver, and an internalpower supply circuit 96 which conditions power from the vehicle data busfor use by the tester. It is preferably a switching power supply whichprovides full operation over 5.1 to 24 VDC input voltage with transientand reverse polarity protection. EPROM 86 constitutes the built-insoftware routines which provide timing sequences and interrupts,processes and decodes the keyboard, places data on display, controlscommunications with the vehicle data bus and provides basic utilitypackages and tester self-test routines.

The display 10 is provided on a separate circuit board and is connectedto the microprocessor bus via the display drivers 100. The ALDLreceptacle J1 provides an interconnection between the ALDL/power supply96. The internal microprocessor bus is brought out on a wire harnessthat terminates at 40 pin connectors in the program cartridge receptacleJ2 and the input/output cartridge receptacle J3. The program cartridgeis shown with a 256 K EPROM 102 and the I/O cartridge with a 128 K EPROM104 which provide appropriate controls to the microprocessor. Theinput/output cartridge is also shown as including an RS232communications interface 106 which, among other things, can be used totest the car from a remote location via communications line 108.

A schematic diagram of the transceiver 92 and multiplexer 94 sections ofthe tester circuitry is given in FIG. 13. The multiplexer section isshown to the right of dashed line 110, and the transceiver section tothe left. Signals to be transmitted to the ALDL connector are receivedfrom the microprocessor on line 112 and transmitted through thetransceiver via an invertor INV1 and voltage divider 114 to the gate ofa field effect transistor FET1 which is protected by a filter capacitorC1. The source of FET1 is connected to ground through resistor R1, whilethe signal to be transmitted to the ALDL is delivered to the multiplexerover lines 116 and 118. Signals received by the multiplexer fortransmission back to the microprocessor enter the transceiver over line120, from whence they are delivered to the inverting input of anoperational amplifier 122. The inverting and non-inverting inputs of OPamp 122 are connected to ground through capacitors C2 and C3,respectively, while the amplifier output is delivered through invertorINV2 to the microprocessor.

The multiplexer has two switching circuits, one connected to theterminal for ALDL L and the other to the terminal for ALDL M. The twoswitching circuits include switching transistors FET2 and FET3,respectively. The gates of these transistors are controlled individuallyfrom the microprocessor such that the switching states of the twotransistors may be alternated or operated in common, as desired. FET2controls another switch FET4, which makes or breaks a connection betweenALDL L and line 118. In a similar manner, FET3 controls another switchFET5 which makes or breaks a connection between ALDL M and line 116. Themultiplexer switches are operated under microprocessor control to bothtransit signals to and receive signals from ALDL.

Turning now to FIG. 14, a block diagram of the circuitry employed by thespecialized input/output module 46 of FIGS. 5-7 is shown. This cartridgeis used to monitor vehicle performance during normal operation away fromthe service center to detect intermittent malfunctions that might notoccur at the service center. A special low power standby control isprovided to keep the tester from draining the vehicle battery when theengine is not running. The tester is connected to the vehicle in a lowpower standby state during which the vehicle's electronic data bus iswatched for changes of state. When data bus activity is detected, thecartridge turns the tester on and monitor the bus for data indicative ofan intermittent malfunction. When a malfunction condition is detected,the cartridge stores both the status of the systems being monitored andthe time at which the reading is taken in memory.

A connection is made to the ALDL/power cable via terminal 124 such thatthe cartridge data bus 126 carries the same signal as the vehicleelectronics data bus. The activity monitor circuit 128 monitors the databus 126 and activates a relay 130 when the data bus becomes activeindicating that the vehicle is running. The closing of relay 130completes a circuit between the tester via terminal 132 and the vehiclepower via terminal 124 to provide operating power to the tester. Vehiclepower is brought into the cartridge via terminal 124 and is applied to astandby power circuit 134 to power the cartridge RAM 138, a time of dayclock 144, and the activity monitor 128. It is also brought to thetester main power relay 130. Upon closing of the power relay, the testerbecomes active and monitors the data it receives on line 126 formalfunction conditions. When a malfunction is detected, the tester logsthe data into a 256 K RAM 138, via line 140 and terminal 142, along withthe value of the time of day clock 144 to log the time at which themalfunction occurred. A battery 136 is provided to keep power on thevolatile RAM 138 when the tester is disconnected from the vehicle. Atiming circuit 146 provides a bit rate of either 9600 or 8192 bits persecond, depending upon the internal vehicle bit rate, to junction 142. Amanual button input circuit 148 is also provided so that data can bestored whenever desired, and an indicator light driver circuit 150 canalso be provided to turn on a light indicating that the cartridge hascaptured data.

A novel vehicle testing system and method has thus been described whichhas four different levels of diagnostic testing. First, it providesmonitoring and control of individual vehicle subsystems for malfunctionisolation supported by the technician's intuitive input. Second, itprovides detailed diagnostic testing in conjunction with the vehiclemanufacturer's service manuals. Third, it offers specialized subsystemtesting by means of specialized diagnostic programs for automaticisolation to the faulty subsystem. Fourth, it provides for thetrouble-shooting of intermittent faults by the diagnostic capture ofdata upon the occurrence of fault conditions. It is much faster thanpresently available testing methods, offers a more comprehensive andaccurate analysis of vehicle malfunctions, and provides much moreflexibility than previous systems. While particular embodiments havebeen shown and described, numerous variations and alternate embodimentswill occur to those skilled in the art. Accordingly, it is intended thatthe invention be limited only in terms of the appended claims.

I claim:
 1. A diagnostic test unit for automobile electronics systems,comprising:an off-vehicle microprocessor, means for selecting andproviding operational controls to the microprocessor during a testsequence, a selectable program means providing a selectable one of aplurality of diagnostic test sequences to the microprocessor forexercising and altering the operation of particular electrical systemsin the automobile, a transceiver which is connectable to provide aninterface between the microprocessor and the automobile electronicssystem, the transceiver providing an interactive path for transmittingtest signals from the microprocessor to exercise and alter the operationof said systems in the automobile, and a receiver path enabling themicroprocessor to monitor the condition of associated automobile systemswhile a first system is being exercised, and a power supply for the testunit.
 2. The diagnostic test unit of claim 1, for an automobile havingan electronics data bus and an associated assembly line diagnostic link,further comprising means for connecting the transceiver with theassembly line diagnostic link to access the electronics data bus.
 3. Thediagnostic test unit of claim 2, for an automobile in which theelectronics data bus is a ring bus and its associated assembly linediagnostic link has a pair of output terminals, wherein the connectingmeans is adapted to connect the transceiver with each of said outputterminals, including a multiplexer connected to multiplex signalsbetween the transceiver and the two output terminals, whereby automobilesystems on the electronics data bus can still be accessed by thetransceiver despite a fault on the bus.
 4. The diagnostic test unit ofclaim 2, wherein the power supply is adapted to receive power from theautomobile's power system via the cigarette lighter socket, and toconvert the received power to a form usable by the tester.
 5. Thediagnostic test unit of claim 2, the transceiver comprising a serialdata link with an impedance substantially matching that of theautomobile electronics data bus.
 6. The diagnostic test unit of claim 1,including a housing for the microprocessor, control means, transceiverand power supply, the housing including a receptacle for receiving aprogram cartridge, the program means comprising one of a plurality ofdifferent program cartridges which are adapted to be removeably insertedinto the receptacle, the various program cartridges beinginterchangeable to program the test unit with different test sequences.7. The diagnostic test unit of claim 6, said housing being portable andcapable of being hand held.
 8. The diagnostic test unit of claim 1,further comprising a display for displaying the test results.
 9. Thediagnostic test unit of claim 1, further comprising means forcommunicating the test results to a remote location and for receivingcontrol inputs from the remote location.
 10. A diagnostic test unit forautomobile electronics systems, comprising:a portable housing, anoff-vehicle microprocessor, a keyboard connected to provide selectableoperational controls to the microprocessor during the course of a testsequence, a receptacle in the portable housing adapted to releasablyreceive interchangeable program cartridges programmed with respectivetest sequences for exercising and altering the operation of particularelectrical systems in the automobile, and to connect a received programcartridge with the microprocessor, a transceiver providing aninteractive interface for two-way testing communication between themicroprocessor and the automobile electronics systems under the controlof the selectable operational controls and the connected programcartridge, and a power supply for the test unit, the portable housingcontaining the above elements and being capable of being hand held. 11.The diagnostic test unit of claim 10, for an automobile having anelectronics data bus and an associated assembly line diagnostic link,further comprising means for connecting the transceiver with theassembly line diagnostic link to access the electronics data bus, and asecond receptacle adapted to releasably receive interchangeableinput/output cartridges for communicating with specified additionallocations in the automobile electronics system.
 12. The diagnostic testunit of claim 10, further comprising a display for displaying the testresults.
 13. The diagnostic test unit of claim 10, further comprisingmeans for communicating the test results to a remote location and forreceiving control inputs from the remote location.